As humans explore space, it’s reasonable to imagine that other beings in the universe are doing the same. Encountering explorers from other planets have been a staple of science fiction for decades. Videotapes from space shuttle missions have persuaded some folks that NASA astronauts have already encountered alien visitors.

On the space shuttle mission STS-48 in September 1991, a TV onboard Discovery spotted moving white dots suddenly changing direction when a flash of light appeared. Although nearby debris frequently appears on shuttle videos, the combination of flares, streaks and changing directions grabbed imaginations. Answering a congressional query the following month on behalf of a curious constituent, NASA had four Houston experts — including one astronaut, astronomer Karl Henize — examine the videos.

“The objects seen are [Discovery]-generated debris, illuminated by the sun,” they reported. “The flicker of light is the result of firing of the attitude thrusters on [Discovery], and the abrupt motions of the particles result from the impact of gas from the thrusters.” That didn’t wash for some viewers, who believed they were seeing alien visitors or Star Wars-like battles. Nearby drifting debris has been hit by jet pulses on other shuttle flights. Here’s an example from STS-63 in February 1995.

Popular Interpretation

Enthusiasm for the UFO interpretation of space pictures isn’t restricted to a narrow band of crackpots, as any Web search demonstrates. Mainstream writers and major TV networks also promulgate these misinterpretations. Aside from enhancing the public’s paranoia about government cover-ups, it can have a poisonous effect on public support for space exploration if a substantial portion of voters becomes convinced by such theories that space experts, astronauts and scientists are lying to them.

Such space tapes are no surprise to NASA; the agency shrugs them off as just one more phenomenon of space flight. The STS-48 images were being collected as part of an ongoing NASA study of unusual lightning. The project was coordinated by NASA scientist Otha “Skeet” Vaughan, in Huntsville, Ala. He has collected and analyzed about 500 hours of tapes over two decades of shuttle flights, probably watching more space video than anyone else.

Just Debris

Vaughan, who retired from NASA last month, said such dots appear frequently. “They’re an ordinary part of space flight,” he says. “It’s obviously just more shuttle debris.” Astronauts aboard the STS-48 mission agree. Mission specialist Mark Brown says ice formed on the shuttle’s main engine bells after the remaining fuel was dumped in space. “These crystals would break free of the engines and float around the shuttle,” he says. “When illuminated by sunlight they looked like small diamonds floating in space, disturbed only when the maneuvering rockets fired — the plumes from the rockets would hit them and send them off in different directions.”

Shuttle co-pilot Ken Reightler says: “We saw a lot of this on STS-48 because we had a dump nozzle that was leaking.” The same nozzle leaked on the shuttle’s next mission and “created the same shower of ice particles — but this time apparently no one misinterpreted them as UFOs.” Space shuttles are often surrounded by clouds of small ice particles from dumped water or leaking jet thrusters.

Fireflies

Small particles flaking off manned spacecraft have been around since John Glenn saw “fireflies” outside his capsule in 1962. Apollo astronauts saw them so often they were nicknamed “moon pigeons.” A NASA study in 1971 traced them to propellant leaks, water dumps, pyrotechnic separation and other ordinary events.

Yet claims for an extraordinary interpretation of the STS-48 images persist, coming from respectable and seemingly rational people. Jack Kasher, a physicist from Nebraska, has published an exhaustive analysis showing why they cannot be debris. “The only feasible explanation,” he concludes, “is that they actually were spacecraft out in space away from the shuttle.” Mark Carlotto, an imaging specialist in Massachusetts, published a 1995 report in the Journal of Scientific Exploration, claiming that “beyond a reasonable doubt” the objects could not be explained as known phenomena.

Shedding Light

Two factors — sunlight and the steering-jet pulses — explain the videotape. The shuttle TV cameras observed lightning on the night side of Earth. But as the shuttle circled toward the day side, it rose into sunlight even while the camera remained fixed on the still-dark horizon behind it. So objects near the shuttle suddenly become illuminated — and it’s precisely at sunrise that the most famous “shuttle UFO videos” show the appearance of these dots. The autopilot normally fires the shuttle’s steering jets to keep the craft on course. Telemetry readouts from STS-48 show exactly such a jet firing at the time of the mystery pulse.

Space junk and thruster gas are a lot less exciting than alien visitors and space battles, so the popularity of UFO explanations for such videotapes will persist. But if recent studies prove anything, it is that the less one knows about space flight, the more likely one is to swallow the idea of space shuttles spotting UFOs.